Process for controlling a multiple cylinder internal combustion engine in the cold start and warming up phases

ABSTRACT

A process is disclosed for controlling a multiple cylinder internal combustion engine in which exhaust gases undergo subsequent treatment. To ensure a gaseous exchange, air is supplied to the individual cylinders through inlet devices and exhaust gases are discharged through outlet or exhaust devices. The inlet and outlet devices are independently driven but their opening and closing times may be synchronized. Beginning in the cold start phase until the warming up phase, fuel is supplied to only part of the cylinders that act as an engine and the supply of fuel to the other cylinders is cut off. The other cylinders work then as compressors. The air volume heated in these cylinders by compression flows through the outlet device into the exhaust gas system and reacts with the exhaust gases.

BACKGROUND OF THE INVENTION

Due to the severe environmental impact of exhaust gas emissions ofinternal combustion engines, the demands with respect to the emissionbehavior of modern internal combustion engines are becoming ever morestringent. In addition to the reduction of exhaust gas emissions throughsecondary measures such as, for example, the use of catalyticconverters, it is also necessary to markedly reduce the untreatedprimary pollutant emission produced by the engine.

In this context, the pollutant behavior is influenced considerably, onthe one hand, by the normal operation with rapid changes in engine rpm'sand changes of the engine load and by the cold engine operation.According to the test cycles for the inspection of engines prescribed bylaw, the first 60 to 80 seconds of the starting phase of a cold engineare decisive for staying below the exhaust emission limits. Up to 80% ofthe unburnt hydrocarbons emitted during the entire test cycle arereleased during this time period at an engine starting temperature of25°. Cold intake pipe walls and combustion chamber walls, the higherfriction loss that must be overcome, and the catalytic converter thathas not yet reached operating temperatures and in which the conversionrates in the cold operating state are still very low are only a few ofthe factors which contribute to a drastic increase in the hydrocarbonemission and the emission of carbon monoxide. At ambient temperaturesbelow 0° C., a further marked increase in the pollutant emission occursduring the cold start and warming-up phases.

A number of options for the reduction of pollutant emissions havealready been implemented which largely only become effective, however,when the engine has reached operating temperatures. In addition tostructural measures such as, for example, cylinder head and combustionchamber design, position of the spark plugs and of the injectionnozzles, number of valves, displacement, stroke-bore ratio, compressionratio, intake port and exhaust port design, the generation of primarypollutants can also be influenced through operative measures. For thispurpose, factors lend themselves such as carburetion, ignition momentand injection moment, control times, internal recirculation of residualexhaust gas through control time changes, external recirculation ofexhaust gas, cutoff of the fuel supply during the overrun phases, andthe use of a phase change material device for the utilization of the"waste heat" of the engine. The hydrocarbon emissions can also bereduced by engine-external measures in the exhaust gas region such as,for example, an after treatment of the exhaust gas through catalyticconverter systems, insulation of exhaust manifold and exhaust gas systemas well as the use of thermal reactors. The engine-external injection ofsecondary air during the cold start and warming-up phases promotes thesecondary reaction of unburnt hydrocarbons and carbon monoxides in theexhaust gas system and additionally results in a more rapid heating upof the catalytic converter due to the heat released during oxidation. Inconventional engines, this takes place by way of an additional secondaryair pump which must be driven by an electric motor or by the internalcombustion engine itself.

SUMMARY OF THE INVENTION

It is now the object of the invention to propose a process forcontrolling a multiple-cylinder internal combustion engine of this typefor the cold start and warming-up phase, which process results in areduction of the pollutant emissions specifically during this operatingphase of an engine.

According to the invention, this object is accomplished by a process forcontrolling a multiple-cylinder internal combustion engine with internalcombustion and after treatment of the exhaust gases, wherein the gasexchange in the individual cylinders takes place through intake devices,at least for the air, and exhaust devices for the exhaust gas, whichdevices can be actuated independently of one another but with openingtimes and closing times that are coordinated with one another, wherein,beginning in the cold start phase up into the warming-up phase, only aportion of the cylinders is supplied with fresh fuel mixture, whichcylinders then function as an engine, and the supply of fresh fuelmixture to the other portion of the cylinders is cut off, whichcylinders then function as a compressor, and the amount of air heated inthese cylinders by the compression process is admitted through theexhaust device into the exhaust gas system for the secondary reaction ofthe exhaust gases. Thus, it is possible to have one or a plurality ofcylinders of the engine work as a "hot secondary air pump" withoutbooster sets and to use the hot air made available by this process forthe secondary reaction of the unburnt hydrocarbons and carbon monoxidesin the exhaust gas system. This becomes possible in that, as a functionof the control times of the intake device and of the exhaust device, ametered air amount can be admitted into the exhaust gas system as neededthrough intake and exhaust devices which can be actuated independentlyof one another but in coordination with one another and with it beingpossible to cut off the injection to the individual cylinders. This cantake place during every crankshaft rotation as well as after severalrotations. Additionally, the high temperature level of the compressedair can be utilized for the more rapid heating of the catalyticconverter and the secondary reaction in the exhaust gas system can bepromoted further if the exhaust valve in the region of the finalcompression phase opens early.

Another advantage is that the cylinders functioning as an engine, whichcylinders must drive the cylinder or the cylinders functioning as acompressor, carry a higher load so that here a more rapid heating of theregions in the proximity of the combustion chamber as well as a morerapid heating of the exhaust gas system takes place through higherexhaust gas temperatures. In a particularly useful embodiment of theinvention, it is provided here that the fuel supply to an individualcylinders is changed over alternatingly. By way of the alternating useof the cylinders as an "engine" and as an "air pump", all cylinders aresuccessively integrated into the engine operation during this phase andare heated according to the higher thermal load, and, thus, a cooling ofthe cylinder walls surrounding the combustion chamber is prevented.Therewith, the risk of the flame going out too early on the coldcombustion chamber walls is counteracted and the hydrocarbon emissionscan be reduced in this manner. With an operating mode of this type, thecosts of and the installation space for an additional secondary air pumpare saved. The fuel can be injected into the air intake channel ordirectly into the cylinder.

In an embodiment of the invention it is provided that, if starting takesplace via an auxiliary drive, the intake devices and/or the exhaustdevices are kept open during the first revolutions. Thus, the startingpower that has to be generated by the auxiliary unit, usually a starter,becomes markedly smaller. This results in smaller auxiliary units forthe starting process which are more advantageous in terms of costs andweight and for which the energy that must be provided and thus the sizeof the battery is then also reduced.

A further advantageous embodiment of the process according to theinvention provides that, in support of the processing of the fuel-airmixture, the intake devices are opened while being respectively adaptedin the direction "late". This prevents the problem of inferiorconditions for the carburetion in internal combustion engines withexternal carburetion during the cold start and warming-up phases. Afterall, the low temperature level of the cylinder charge and of the intakechannel walls markedly impairs the atomization quality of thecarburetor. By means of the embodiment proposed by the invention, thecarburetion process can now be improved considerably by way of a lateopening of the intake devices. By way of an unconventional "late intakeopens", the intake device opens only when the piston approaches thelower dead center during the downward movement. During opening of theintake device, a pronounced acceleration of the air column commenceswith the already injected fuel because of the then prevailing vacuum inthe combustion chamber. The large relative movement between fuel and airas well as the increased movement of the mixture in the combustionchamber promote the processing of the mixture and result in a markedlyimproved combustion. During the further phase of the engine warm-up, aconventional operating point-dependent optimization of the residualexhaust gas portion can then improve the warming-up process by acombinatorial system of the valve control parameters "intake opens" and"exhaust closes". Through an "early exhaust opens", the temperature inthe exhaust gas system is additionally increased through the outflowinghot exhaust gases. By adapting the control time "exhaust opens", thesecondary reactions in the exhaust gas system as well as the heating-upphase for the catalytic converter can be shortened.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in greater detail by means of schematicdrawings of an embodiment in which:

FIG. 1 is a wiring and control diagram for a cylinder of amultiple-cylinder internal combustion engine;

FIG. 2 is a flow diagram;

FIG. 3 is a mass flow diagram for a late opening intake device;

FIG. 4 illustrates the inflow rate of the air into a cylinder having twointake devices which can be actuated independently of one another.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic illustration of a partial section through thecombustion chamber of a cylinder of a multiple-cylinder internalcombustion engine. A piston 2 moves in the cylinder tube 1. An intakedevice 3.1 and an exhaust device 3.2 are provided in the cylinder head,both devices being respectively provided with an actuating device 4.1and an actuating device 4.2 by means of which the intake device orexhaust device can be respectively opened and closed. The actuatingdevices, which may be configured, for example, as actuating devices thatare operable electromagnetically, are connected to a control logic 5 inwhich are stored characteristic engine diagrams for different operatingstates in the form of control times for the intake and exhaust devicesas well as for the fuel injection and the ignition. These data arecalled up based on the control input 6, the rpm information 7, theengine temperature 8, the cooling water temperature 9 of the pressure 10and the temperature 11 of the combustion air, and they are supplied toan amplifier stage 12 for the actuation of the intake and exhaustdevices, the injection nozzle 13 and the ignition 14 corresponding tothe engine cycle. This generates an air mass flow 15 through the filter16 in the throttle-free intake pipe 17 and the fuel flow 18 from thefuel tank via the pump 19 and the pressure control valve 20. The controllogic 5 now has an engine characteristic diagram "cold start phase"which is designed such that, during the cold start phase, the fuelsupply to individual cylinders can be switched off and the control timesof the intake device 3.1 and of the exhaust device 3.2 can bepredetermined while deviating from the normal operating control times.

The control during this cold start phase and the subsequent warming-upphase is explained in greater detail in FIG. 2 by way of a four-cylinderengine. On the suction side, the individual cylinders I, II, III and IVare provided with intake pipes 17.1, 17.2, 17.3 and 17.4, respectively,into which merges a corresponding injection nozzle 13. The hot exhaustgases leaving the individual cylinders are carried away via an exhaustpipe 21 in which a catalytic converter 22 is arranged.

During a cold start of this internal combustion engine, the intakedevices 3.1 as well as the exhaust devices 3.2 to all cylinders arefirst kept open via the control logic 5 so that the engine can be setrotating via the electric starter by means of a small force expenditure.After the detection of a predetermined minimum rpm, the intake devicesand the exhaust devices of the individual cylinders are put intooperation in conformity with the stroke; but during this process, fuelis only injected into the intake pipes 17.2 and 17.3 to the cylinders IIand III, and the ignition is added according to the working cycle sothat only the cylinders II and III function as engine. The cylinders Iand IV only take in air which is compressed according to the workingcycle and heated during this process. Accordingly, hot exhaust gasenters the exhaust gas pipe 21 from the cylinders II and III functioningas an engine in accordance with the working cycles, and hot air entersthe exhaust gas pipe 21 from the cylinders I and IV functioning as acompressor. Since cylinders II and III must also do the work of thecompressor of cylinders I and IV, they are more heavily charged becauseof the work that is to be performed so that this results in an exhaustgas that not only is hotter but contains a high portion of unburnthydrocarbons and of carbon monoxides during the first working cyclesbecause of the unfavorable temperature conditions. But since hot airenters the exhaust gas pipe from cylinders I and IV at the same time,the catalytic converter 22 is heated up faster due to the reaction heatof the secondary reaction, and the hydrocarbon and carbon monoxideemission is reduced. The higher exhaust gas temperatures cause thenecessary secondary reactions for the decomposition of the unburnthydrocarbons as well as of the carbon monoxide to start much earlier.

Because of the fact that the intake devices and the exhaust devices ofthe individual cylinders can be actuated independently of each other,the switching can now be effected via the control logic 5 during thisfirst starting phase in such a manner that the cylinders II and III donot exclusively function as an engine and the cylinders I and IV as acompressor, but that the cylinders respectively function alternately asan engine or a compressor. This then accomplishes that all cylindersreach their operating temperature much faster and that, ultimately, thepollutant emission during the starting phase is reduced because theentire system is heated up much more quickly.

Since the individual intake and exhaust devices can be actuated in avariable manner, it is also possible for the cylinders that respectivelywork as an engine to improve the carburetion even in the cold state.FIG. 3 illustrates the mass flow through an intake device as a functionof the crank angle. The dashed line shows the mass flow for aconventional throttle control. If, in line with the design of theprocess according to the invention, the intake device 3.1 isrespectively opened when the piston approaches the lower dead centerposition during the downward motion, a very considerable vacuum iscreated in the cylinder so that the amount of air to be taken in mustflow into the combustion chamber within a short time, i. e., at a highspeed, so that a considerable swirl takes place. The associated massflow for this specific actuation of the intake device is illustratedschematically in FIG. 3 with an unbroken line in comparison to thenormal throttle control.

Furthermore, starting from the cold start phase up to the normaloperating phase, FIG. 4 illustrates, for different operating states, theintroduction speed of the fuel-air mixture into a combustion chamber ofan engine having two intake devices per cylinder. Again, the intakedevices can be actuated independently of one another, with it beingpossible that at least one intake device can work with two differentstrokes.

During engine start-up, respectively one intake device is closed and theother intake device is operated with a reduced stroke for the cylindersoperating in the engine mode. This then results in an intake speed forthe fuel-air mixture as a function of the engine load as is indicatedschematically by the curve a. As the heating up of the engine progressesand based on the predetermination of the control logic 5, the actuatingdevice 4 of the working intake device 3 is changed over to full strokeso that, based on the larger cross section, the inflow speed is reduced,as is shown schematically in curve b. As soon as the engine has reachedits operating temperature, the second intake device, which was keptclosed until now, can then also be operated with its full stroke as afunction of the operating point so that this results in the introductionspeed of the fuel-air mixture into the combustion chamber indicatedschematically by curve c. Via the control logic 5, the moment "intakeopens" will also be adapted to the operating point in accordance withthe changing operating data of the engine during the warming-up phase.In an internal combustion engine having two intake devices, as describedabove, the moment "intake opens" may but must not be shifted in themanner described by FIG. 3.

While the smooth running is diminished in a four-cylinder engine due tothe possible actuation of respectively only one cylinder in the pumpingmode, engines having a greater number of cylinders can be actuated suchthat, apart from a change from engine mode to pumping mode of therespective cylinders, a continuous addition of cylinders in the pureengine mode is also possible selectively and adapted to the operatingpoint. The amount of air pumped in the pumping mode can be furtheradjusted via the number of cylinders functioning as pump and/or via thecontrol of the intake times of the intake devices. The state ofaggregation of the pressure temperature of the air that is released intothe exhaust gas system can be influenced via a corresponding actuationof the exhaust device.

As an actuating device for the independent actuation of the intake andexhaust devices, the use of electromagnetic actuating devices isparticularly advantageous, as known, for example, from DE-A-30 24 109.As long as the two solenoids are deenergized, the intake devices arekept open via the associated armature in a mean position between anopener and closer coil via two spring elements acting counter to oneanother. During operation, the armature then oscillates back and forthbetween the opener and closer coil. This means that the control time canbe predetermined exclusively by the control logic 5 in a mannerindependent of the crank angle via the corresponding actuation of theexcitation currents to the individual coils. Thus, it is also possibleto keep the intake device and the exhaust device open for all cylindersvia an auxiliary unit while the engine is still turning, just as it ispossible to coordinate the opening and closing times of the intakedevices and of the exhaust devices with one another in any desiredcombinatorial system depending on the operation. As the heatingprogresses, it is also possible therewith to transition into theoperating phase from the above-described actuation process for the coldstart phase via the control logic 5 and the characteristic enginediagrams stored therein, in which operating phase the intake devices andthe exhaust devices can be actuated in a manner in which they areload-dependent with respect to their control times and adapted to oneanother.

We claim:
 1. A process for controlling a multi-cylinderinternal-combustion engine with internal combustion and subsequenttreatment of exhaust gases, wherein the engine has a plurality ofindividual cylinders in which gas exchange occurs, each cylinder havingan intake device for introducing air into the cylinder and an exhaustdevice for removing exhaust gas from the cylinder, and an engine controlwhich actuates the intake and exhaust devices independently of oneanother but with opening times and closing times that are coordinatedwith one another, wherein the process, beginning in the cold start phaseup to the warming-up phase, comprises the steps of:supplying only aportion of the cylinders with fuel, the fuel-supplied cylindersoperating as an engine; cutting off the supply of fuel to the otherportion of the cylinders so that such cylinders operate as compressors;introducing air heated in the cylinders operating as compressors intothe exhaust gas system by an adaptable control of the exhaust system,said introduced air being one of changeable quantity, changeablepressure, and changeable temperature for the secondary reaction of theexhaust gases; and opening the intake devices of the cylinders that areoperating as an engine late for improving the fuel/air mixture.
 2. Aprocess according to claim 1, wherein the fuel supply and the ignitionto the individual cylinders is changed over alternately.
 3. A processaccording to claim 1, wherein, during startup via an auxiliary drive, atleast one of the intake devices and the exhaust devices is kept openduring the first revolutions.
 4. A process according claim 1, wherein,in support of the processing of the fuel-air mixture, the intake devicesare opened while being respectively adapted in the direction "late". 5.A process according to claim 1, wherein in the cold start and warming-upphases the passage cross sections of at least one of the intake devicesand the exhaust devices are reduced.